This invention relates to a harmonization control system for performing a control for harmonizing movements of plural shafts and, more particularly, to a novel harmonization control system capable of performing a control for harmonizing movements of an extremely large number of shafts such as hundreds of shafts.
Among industrial machines employing a servo system such as robots, there is one which controls movement of an object of control by cooperative movements of plural shafts. When, for example, an object of control (e.g., an arm of a robot) is moved in two dimensions, a two-shaft servo control is performed and when it is moved in three dimensions, a three-shaft servo control is performed. In this case, a synchronization control is made for controlling a two-dimensional or three-dimensional locus of movement of the object of control. In other words, a control is made for synchronizing movements of plural shafts at each moment so that a desired locus will be produced by cooperation of the respective shafts.
In a synchronization control, however, a desired multi-dimensional locus of movement such as two-dimensional or three dimensional locus of movement must be subjected to vector analysis for computing an expected movement pattern of each shaft. This requires an extremely complicated control with resulting limitation in the number of shafts which can be synchronously controlled. That is, it is only possible to synchronously control three shafts at most.
With a robot having a large number of arms, there is a case where movements of these arms are desirably controlled in association or harmonization with one another. As movements of a robot become more and more elaborate or complicated, such demand for associated or harmonized movements of arms is expected to grow stronger and stronger from now on. In not only robots but also in a production line having a large number of actuators which are desirably moved in association or harmonization with one another, it is desirable to control these large number of actuators in association or harmonization with one another. Also, in theaters, various stage settings such as rising stage and a curtain have come to be servo-driven by actuators. In this case, it is desirable to control a large number of actuators for moving these stage settings in association or harmonization with one another, because an excellent stage effect will be produced if these large number of actuators are controlled properly in association or harmonization with one another in accordance with a certain factor.
The conventional synchronization control method does not give an effective solution to such demand, since, as described above, the number of shafts which can be synchronously controlled is limited to a very small number. In the newest theater, for example, hundreds of actuators are provided and it is utterly impossible to achieve synchronized movements of these hundreds of actuators by the conventional synchronization control method.
It is theoretically possible to prepare programs of movement patterns of respective shafts so that the respective shafts move in synchronization with one another in a desired mutual relation and cause these shafts to be moved synchronously by performing a control for driving the respective shafts in accordance with these programs. In a case, however, where the number of shafts to be controlled synchronously amounts to several hundreds, it is almost impossible to program respective movement patterns so that movements of the respective shafts will correlate with one another having regards to all mutual relations of these shafts. Even if it is possible at all, such programming will require tremendous amount of work and cost and will not pay in terms of the cost.
Besides, loop gains of control loops in drive control units of respective shafts differ from one another and vary from time to time due to difference in load condition among the respective shafts and timewise variation in load condition of the respective shafts. However, the control according to the movement patterns programmed as desired, per se, cannot cope with such difference or variation in loop gains.